Appling the mixed sludge of raw sludge and waste activated sludge from sewage waste water treatment plant, this paper studies the factors during aerobic digestion process.

Sludge bulking is a hard job in activated sludge treatment, especially in the treatment of high load waste water from petrochemical plant.

Sludge water content has been detected as the index to indicate the effect of ultrasonic and composite flocculants on the residual activated sludge in petrochemical water treatment plants.